Chapter 2: Section 3

1. Chapter 2: Section 3 Internal Forces shaping the Earth &

2. A Human Perspective • Sally Ride, America’s first female astronaut, wrote the following after one of her trips into space: • “I also became an instant believer in plate tectonics; India really is crashing into Asia, and Saudi Arabia and Egypt really are pulling apart, making the Red Sea even wider. Even though their respective motion is really no more than mere inches a year, the view from overhead makes the theory come alive.” • From space, ride was seeing evidence of the internal forces that have shaped the earth’s surface.

3. Plate Movement • Most Scientists assume that the force is a process called convection. Convection is a circular movement caused when a material is heated, expands & rises, then cools & falls. This process is thought to be occurring in the hot, pliable mantle rock beneath the plates

4. The Earth’s Major Plates

5. The Earth’s surface is elastic. Physical geographers now know that Earth’s crust is broken into a series of huge, rigid slabs or Plates, some of them as large as continents. The movement of these plates is called Plate tectonics. They shape our land. Tectonics plates move in one of four ways: Divergent boundary: Plates move apart or spread. Convergent boundary: (subduction)Plates collide with each other, causing one plate to either dive under or ride up over the other plate. Convergent (Collision): Crashing into one another resulting in the formation of mts. Transform Boundary: Plates slide past one another. Plate Tectonics

6. Seafloor Spreading • After WWII, scientists began to use sonar to map the floor of the Atlantic Ocean. They also began to investigate the age of the rocks on the seafloor as well as other features of the ocean landscape. • Ex: Mid-Atlantic Ridge, & Pacific Rim, some of these ridges emerge as islands. • The theory of seafloor spreading is that molten rock from the mantle rises under the mid-oceanic ridge and breaks through the rift. As the seafloor moves away from the ridge, it carries older rocks away.

7. Seafloor spreading (Divergent) is the movement of two oceanic plates away from each other, which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a a mid-ocean ridge. Seafloor Spreading

8. Oceanic Plate and Continental Plate: can cause volcanoes Two Oceanic Plates: same, one may be push under & cause magma activity Two Continental Plates: Create mts Convergent: Subduction

10. When plates grind or slip past each other at a fault the earth shakes or trembles. Seismograph will measures the size of the waves created by an earthquake. Richter Scale uses information collected by a seismographs to determine the relative strength of an earthquake. San Andrea fault line in California. Earthquakes

11. A tsunami is a very large sea wave that is generated by a disturbance along the ocean floor. This disturbance can be an earthquake, a landslide, or a volcanic eruption. A tsunami is undetectable far out in the ocean, but once it reaches shallow water, this fast-traveling wave grows very large. Tsunami

12. Volcanism • Heat from the upper levels of the mantle forces its way to the surface at weak places in the Earth’s crust leading to volcanism. • When magma erupted through the surface it is called lava.

13. Hot Spots: Mantle thermal plumes • In 1963, J. Tuzo Wilson, the Canadian geophysicist who discovered transform faults, came up with an ingenious idea that became known as the "hotspot" theory. Wilson noted that in certain locations around the world, such as Hawaii, volcanism has been active for very long periods of time. This could only happen, he reasoned, if relatively small, long-lasting, and exceptionally hot regions -- called hotspots -- existed below the plates that would provide localized sources of high heat energy (thermal plumes) to sustain volcanism.

15. Ring of Fire: a zone around the rim of the Pacific Ocean, is the location of vast majority of active volcanoes.